The present invention relates to vibration test arrangements and more particularly vibration test arrangements utilised with regard to components such as aerofoils utilised in rotors of a gas turbine engine.
It will be understood that a large number of components require testing to determine their performance in use. One form of testing is fatigue testing and in particular high cycle vibration fatigue testing. With respect to some components such as low pressure compressor blades, eg fan blades, in gas turbine engines their size and thus motions during testing can be severe. It is known to provide isolator devices to assist with respect to high cycle vibration fatigue testing of components and particularly with respect to components having an aerofoil shape. An aerofoil is held in a specific fixture and can be excited in a number of ways and in a particular mode of vibration. Any mode of vibration higher than the first fundamental mode will have node lines which are stationary when the vibration mode is excited. The isolator device is used to inhibit other modes of vibration and isolate the mode of vibration of interest by resting against the node line on the aerofoil so causing that part of the aerofoil to be stationary encouraging the mode of vibration of interest to be excited when the method of excitation is switched on.
FIG. 4 illustrates a typical prior test arrangement 1 for an aerofoil 2 of a blade component. Two isolator devices 3, 4 are located upon a node line 5 of a mode of vibration of interest. As indicated above the isolation devices 3, 4 are presented upon the node line 5 in order to isolate the mode of vibration of interest. The prior isolation devices 3, 4 act against parts of the aerofoil 2 and must absorb relatively large values of vibration energy as well as untwisting actions along the node line 5 during motion of the aerofoil 2. As indicated above the aerofoil 2 is generally a low pressure compressor blade, eg a fan blade from a gas turbine engine. The isolation devices 3, 4 comprise an elastomeric and typically rubber element having a cut edge or point to engage the aerofoil 2. The elastomeric element is held in a rigid clamp for presentation to the aerofoil 2.